Device limiting the delivery output of a jack

ABSTRACT

A device for limiting the delivery output of a jack having a complementary chamber of substantially smaller diameter opening into the end of a main delivery chamber, the complementary chamber having a delivery conduit, a deformable member coupled in translation with a piston rod and being capable of abutting the piston, the deformable member being capable of penetrating into the complementary chamber from the main delivery chamber and being of slightly smaller diameter and having complementary walls with respect to the walls of the complementary chamber to form a passage between the end of main delivery chamber and the complementary chamber, the deformable member being deformed by fluid pressure to increase the transverse section of the passage between the walls of the deformable member and the complementary chamber.

'[ 1 Jan. 22, 1974 DEVICE LIMITING THE DELIVERY OUTPUT OF A JACK [75] Inventor: Louis E. Martin, Senlis, France [73] Assignee: Societe Anonyme Poclain, Le

Plessis-Belleville, Oise, France 22 Filed: May 3,1972

21 Appl.No.:249,879

[30] Foreign Application Priority Data France 91/396 Primary Examiner-Paul E. Maslousky Attorney, Agent, or Firm-Fitzpatrick, Cella, Harper & Scinto [57] ABSTRACT A device for limiting the delivery output of a jack having a complementary chamber of substantially smaller diameter opening into the end of a main delivery chamber, the complementary chamber having a delivery conduit, a deformable member coupled in translation with a piston rod and being capable of abutting the piston, the deformable member being capable of penetrating into the complementary chamber from the main delivery chamber and being of slightly smaller diameter and having complementary walls with respect to the walls of the complementary chamber to form a passage between the end of main delivery chamber and the complementary chamber, the deformable member being deformed by fluid pressure to increase the transverse section of the passage between the walls of the deformable member and the complementary chamber.

5 Claims, 4 Drawing Figures PATENIEum2-2m4 I airs-6724 sum 2 m2 l DEVICE LIMITING THE DELIVERY OUTPUT OF A JACK The present invention relates to a device for limiting the delivery output of a jack.

In order to avoid the piston of a jack coming sharply into abutment on the base of the cylinder, at the end of its stroke, it is known to provide said jack with a device limiting the speed of said piston, which acts only at the end of stroke thereof.

As is known, the fluid which remains to be delivered is laminated in a complementary chamber of section smaller than the section of the main delivery chamber. In this way, the delivery output of the jack is limited.

It is obvious, and this has been measured, that the pressure of the fluid reaches very high values at the level of the complementary chamber. This state of affairs is a serious disadvantage, since the excess pressures developed are so great that permanent deformations of the cylinder are often ascertained, this requiring replacement of said cylinder.

It has therefore appeared necessary to propose a new device limiting the delivery output of a jack, which acts with a hitherto unknown progressiveness.

It is an object of the invention to provide a device limiting the delivery output of a jack, constituted by a complementary chamber which is made in the cylinder of the jack, is disposed at the end of said cylinder, which is in communication with the main delivery chamber of the jack, opens out into the extreme crosssection of said main chamber and possesses a crosssection perpendicular to the axis of the cylinder, substantially smaller than that of the main camber, and by an element in the form of a shoulder which is coupled in translation with the rod of the piston of the jack, is capable of abutting on said piston, by being disposed on the side of this piston which defines the main delivery chamber, possesses a cross-section perpendicular to the axis of the cylinder, slightly smaller than that of the complementary chamber and of complementary form, and is capable of penetrating into said complementary chamber, whilst the delivery conduit of the jack itself opens out into this complementary chamber.

At least one of the two members, element in the form of a shoulder and walls defining the complementary chamber, may be deformed under the action of the pressure of the fluid, whilst said possible deformation corresponds to an increase in the section of the passage connecting the main chamber to the complementary chamber, said passage itself being constituted by the volume defined by the parts of walls of the element and the complementary chamber which are opposite one another and which are included between the extreme cross-sections of the main chamber and the shoulder of the element.

The deformable member is advantageously made of an elastic material.

It is also judiciously provided to be distinct from the piston rod and/or cylinder structure, to which it is coupled in translation.

In a preferred embodiment, this member is constituted by a ring, of which the walls parallel to the axis of the cylinder are deformable, and which defines with the walls of the complementary chamber a passage for the fluid, the section of which varies as a function of the stresses due to the pressure of said fluid.

As a variant, the deformable member is constituted by a ring of revolution whose generatrix has an initial section which may be deformed into a configuration which is in relationship with the value of the delivery output corresponding to the instantaneous position of the piston of the jack in the cylinder.

The invention will be more readily understood upon reading the following description with reference to the accompanying drawings, in which:

FIG. 1 is an axial section through a jack provided with a known output limiter.

FIG. 2 is a part axial section through a jack providedwith an output limiter according to the invention.

FIG. 3 is a variant of the limiter shown in FIG. 2; and

FIG. 4 shows the curves relative to the deceleration of the piston obtained by adapting the limiters of FIGS. 2 and 3 respectively.

FIG. 1 shows a jack of known type, constituted by a cylinder 1 inside which a piston 2 is mounted to slide along axis 3 of said cylinder 1. A sealing joint 4 is interposed between the wall of the cylinder 1 and the piston 2.

Furthermore, a piston rod 5 is integral with the piston 2 and traverses the base 6 of the cylinder 1 with the interposition of a sealing joint 7. It will be noted that a chamber 8, called main delivery chamber, is defined by the piston 2 and the walls of the cylinder 1, and communicates with the outside of the jack by a delivery conduit 9. I

Moreover, it will be noted that a complementary cylindrical chamber 10, coaxial to the axis 3, is disposed at the end of the main chamber 8, whilst the conduit 9 opens out into said chamber 10. The section of chamber 10, which is that of a circular crown, of large diameter D and. of small diameter equal to that of the rod 5, is notably smaller than that of the main chamber 8.

Finally, a shoulder 11, of diameter d slightly smaller than diameter D is integral in translation with the piston 2 and, being located on the side of the face 2a of said piston 2, which defines the main chamber 8, and being disposed coaxially to the axis 3, is capable of penetrating into the chamber 10, at the end of stroke of the piston 2.

FIG. 2 shows most of the elements already referenced in FIG. 1. In this FIG. 2, the shock-absorbing element is in the position in which it effectively acts to reduce the speed of displacement of the piston of the jack.

The piston 2 is maintained integral in translation with the piston rod 5, abutting, by its face 2a, on a shoulder 12 integral with said rod 5, whilst a nut 13 cooperates with the threaded end 14 of the rod 5 in order to maintain the face 2a in contact with the shoulder 12.

It will be noted that the shoulder 11 is constituted by the extreme cross-section of a ring 15, which is integral in translation with the piston rod 5, being fixed axially between a shoulder 16 of said rod 5, and the face 2a of the piston 2. The ring 15 is cylindrical and defines an inner volume 18 by its walls 17 parallel to axis 3, as well as by its wall terminating by shoulder 11, and with the face 2a of the piston 2.

The ring 15 is thus distinct from the rod 5 of the piston and is interchangeable. Moreover, it is made of an elastic material and may, under the effect of the pressure of the fluid contained in the chamber 8, be deformed elastically, in the sense of an instantaneous, provisional reduction in the diameter d of the outer faces of the walls 17. Finally, a conduit 19 traverses one of the walls of the ring 15 and connects the inner volume 18 to the complementary chamber 10.

It will be specified, as a variant, that it would have been possible to retain a rigid shoulder integral with the rod of the piston, but then to dispose a deformable ring similar to ring mentioned above, as walls defining the complementary chamber 10, the essential being, as will be seen, to arrange a member that is deformable at the moment of the end of stroke of the piston, but distinct from the main body of the cylinder 1 itself.

Furthermore, according to another embodiment shown in FIG. 3, the above-mentioned ring is replaced by a ring 15a, the outer walls 17a of which are defined by a non-cylindrical surface of revolution. On this subject, it will be noted that, in both cases, the deformations of the rings 15 or 15a may vary as a function of the actual position of the piston 2 in the cylinder 1, said position being referenced in the present case by the distance L which separates the end cross-section 8a of the chamber 8 from the shoulder 11.

FIG. 4 shows the curves l5 and 15a providing the correspondence between the delivery output Q of the fluid, thus the speed V of the piston 2, and the distance L, for jacks provided, one, with the ring 15, the other with the ring 150.

The functionings obtained in the course of use of the jacks which have just been described, will now be seen.

When the piston 2 of the jack of FIG. 1 approaches the end of its stroke, the shoulder 11 arrives firstly at right angles to the terminal cross-section 8a of the chamber 8. The fluid still contained in said chamber 8 can then only be delivered through the passage between the cylindrical wall of the shoulder 11 (of diameter d) and those of the complementary chamber 10 (of diameter D). As D is only slgithly greater than d, said passage is narrow and, in any case, is of a section considerably smaller than that of the free chamber 10. The result of this arrangement is that the fluid is delivered only after a slow lamination flow, which brings about an increase in pressure in the chamber 8. This pressure, applied to the face 2a of the piston 2, produces a stress in direction opposite the displacement of the rod, thus a braking stress. In the case of the speed of the rod of the jack being consecutive to the drive by inertia of a given mass, this brake stress corresponds to a deceleration of the movement, thus to a reduction in speed, before stopping by mechanical shock is produced.

Unfortunately, the value reached by the pressure is a function of a number of parameters and is governed by the physical laws of fluid flow between narrow walls. Mention will be made, inter alia, of the influences of the viscosity of the fluid along the narrow passage, the output of fluid from chamber 8 to chamber 10, the difference in the diameters D and d. In certain cases, the value reached by the pressure is considerable and the stresses of the pressure on the walls of the cylinder 1 bring about a permanent deformation of said cylinder and consequently the destruction of the jack, no longer by mechanical shock, but by excessive manometric stress.

In order to avoid this disadvantage, which is finally as serious as destruction by mechanical shock, it is judicious to adopt the embodiments according to the invention, described for example in FIGS. 2 and 3, or like embodiments. With the jack of FIG. 2, the increase in pressure, at the end of stroke of piston 2, has for its effect to deform the ring 15 in the sense of reducing the diamter d, thus of increasing the section of passage between the bore of diameter D and the ring of diameter d. Whatever the values of the other parameters, the resultant pressure of the fluid contained in the chamber 8 is thus limited to a suitable value, and particularly beyond the values considered as limiting for the nondeterioration of the jack, which were previously exceeded. However, a deceleration is still obtained due to the lamination of the fluid between the cylindrical walls of the complementary chamber 10 (of diameter D) and the shoulder 11 (of diameter d).

It will have been noted that, even if there is permanent deformation, it is now only the ring 15 which is concerned. The complete jack is thus no longer destroyed, but only a complementary element which is much less expensive to replace.

Furthermore, it will be noted that it is obviously advantageous to have provided the ring 15 to be removable, this facilitating possible replacement thereof, and to have chosen said ring to be of elastic material, this, in the majority of cases, avoiding permanent deformation of said ring, and thus avoiding replacement itself.

Finally, it is obvious that the conduit 19 enables the fluid to be present on the two sides of the ring 15, and thus obtains a balancing of the pressures during established operation. This arrangement therefore permits a choice of moderate dimensions for the ring 15. Of course, the transfer of fluid through said conduit 19, taking into account the deformation of the ring 15, brings about only a small difference in pressure of the fluids contained in the chambers 10 and 18, being given the value of the variation of the volume of the chamber 18, which is very low.

Moreover, the embodiments of either FIG. 2 or FIG. 3 may be adopted, this making it possible, as a function of the instantaneous position of the piston 2, referenced by distance L, to obtain a more or less energetic braking, as shown in FIG. 4.

What is claimed is:

1. A device for limiting the delivery output of a jack having a cylinder, a piston mounted in said cylinder, said piston and cylinder forming a main delivery chamber, a piston rod extending from said piston through said main delivery chamber, said device comprising a complementary chamber formed in said cylinder at the end thereof, said complementary chamber opening into the end of said main chamber and having a crosssection perpendicular to the axis of the cylinder substantially smaller than the cross-section of said main chamber, said complementary chamber having a delivery conduit, a deformable member coupled in translation with said piston rod and being mounted on the side of said piston defining the main delivery chamber and being capable of abutting said piston, said deformable member being capable of penetrating into said complementary chamber from said main delivery chamber, said deformable member having walls and a shoulder at its end opposite said piston, said deformable member having a cross-section perpendicular to the axis of the cylinder slightly smaller than the cross-section of the complementary chamber and the walls of said deformable member being of complementary form with respect to the walls of the complementary chamber to form a passage between the main delivery chamber and said complementary chamber extending between the end of the main chamber and the shoulder of the deformable member, said walls being radially unsupported along its center portion of its length, said deformable member being deformed by fluid pressure to increase the transverse section of the passage between the walls of the deformable member and the complementary chamber.

2. A device according to claim 1 wherein the deformable member is made of an elastic material.

3. A device according to claim 1 wherein the deformable member is constituted by a substantially cylindrical ring, of which the walls parallel to the axis of the cylinder are deformable, and which defines with the walls of the complementary chamber a passage of fluid, the section of which varies as a function of the stresses due to the pressure of said fluid.

4. A device according to claim 1 wherein the deformable member is constituted by a ringof revolution, the generatrix of which possesses an initial section which may be deformed into a configuration which is in relationship with the value of the delivery output corresponding to the instantaneous position of the piston of the jack in the cylinder.

5. A device according to claim 1, wherein said deformable member is separable from said jack, whereby said deformable member is interchangeably replaceable. 

1. A device for limiting the delivery output of a jack having a cylinder, a piston mounted in said cylinder, said piston and cylinder forming a main delivery chamber, a piston rod extending from said piston through said main delivery chamber, said device comprising a complementary chamber formed in said cylinder at the end thereof, said complementary chamber opening into the end of said main chamber and having a cross-section perpendicular to the axis of the cylinder substantially smaller than the cross-section of said main chamber, said complementary chamber having a delivery conduit, a deformable member coupled in translation with said piston rod and being mounted on the side of said piston defining the main delivery chamber and being capable of abutting said piston, said deformable member being capable of penetrating into said complementary chamber from said main delivery chamber, said deformable member having walls and a shoulder at its end opposite said piston, said deformable member having a crosssection perpendicular to the axis of the cylinder slightly smaller than the cross-section of the complementary chamber and the walls of said deformable member being of complementary form with respect to the walls of the complementary chamber to form a passage between the main delivery chamber and said complementary chamber extending between the end of the main chamber and the shoulder of the deformable member, said walls being radially unsupported along its center portion of its length, said deformable member being deformed by fluid pressure to increase the transverse section of the passage between the walls of the deformable member and the complementary chamber.
 2. A device according to claim 1 wherein the deformable member is made of an elastic material.
 3. A device according to claim 1 wherein the deformable member is constituted by a substantially cylindrical ring, of which the walls parallel to the axis of the cylinder are deformable, and which defines with the walls of the complementary chamber a passage of fluid, the section of which varies as a function of the stresses due to the pressure of said fluid.
 4. A device according to claim 1 wherein the deformable member is constituted By a ring of revolution, the generatrix of which possesses an initial section which may be deformed into a configuration which is in relationship with the value of the delivery output corresponding to the instantaneous position of the piston of the jack in the cylinder.
 5. A device according to claim 1, wherein said deformable member is separable from said jack, whereby said deformable member is interchangeably replaceable. 